The present invention relates to a new class of organometallic catalysts, to the process for preparation thereof and their use for the polymerization and copolymerization of ethylene and alpha-olefins in industrial production plants.
In EP 416815 and EP 420436 there is the description of a new type of organometallic catalysts in which a transition metal is coordinated to a cyclopentadienyl ring and a heteroatom. These organometallic compounds, when they are activated with alkylaluminoxanes, are able to produce ethylene polymers with high molecular weight and narrow distribution of molecular weight. They moreover own a great effectiveness in comonomer incorporation. However, when the comonomer content of the polymeric chain is increasing, the molecular weight sensibly decreases (though in these patents there is the description of some synthetic methods to obtain this new type of organometallic complexes, these methods are not useful to prepare the compounds of general formula I).
The use of the catalysts described in patents EP 416815 and EP 420436 is limited to solution processes and mass processes at high temperatures and pressures. The homogeneous catalytic systems have the disadvantage that when they are used in suspension polymerization processes, a part of the produced polymer adheres to the reactor walls: this effect is technically called "reactor fouling". Besides, in most cases, the obtained polymers have a very small particle size and low apparent densities, limiting the industrial production. In order to avoid the reactor from fouling and obtain polymers with high apparent density, the homogeneous systems must be heterogenized on an organic or inorganic support.
Some techniques for heterogenizing organometallic complexes on inorganic supports are based on the simple adsorption of the organometallic compound onto the inorganic support [S. Collins Macromolecules 25, 1780(1992) and J C W Chien J. Polym. Sci., Part A: Polym. Chem. 29, 1603 (1991)]. This process has the disadvantage that the union between the organometallic complex and the inorganic support is not very strong, as there can be loss of the organometallic compound during the polymerization process, causing the fouling of the polymerization reactor. Other processes are based on the modification of the inorganic support with methylaluminoxane before the incorporation of the organometallic complex (EP 668295, WO 9205203, WO 9407928 and WO 9403506), but they have the disadvantage that the obtained solid catalysts must be activated with additional quantities of aluminoxane for its use in polymerization. Besides, the obtained polymers apparent densities are not as good as it would be desirable.
As a consequence, there is the need for heterogenization processes that advantageously exceed those described in patents EP 668295 and WO 9403506. The problem can be solved by the introduction of a reactive halogen in the bridge of the organometallic complex, producing new complexes, that can be advantageously used in order to obtain heterogeneous catalytic systems prepared by a chemical reaction with an organic or inorganic support as described in EP 757992. Besides these catalysts produce polymers with a good apparent densities.
Therefore an object of the present invention is the production of new organometallic complexes whit a reactive halogen in the bridge and their heterogenization on an organic or inorganic support.
Further object of the present invention is a suitable method for the preparation of said complexes. This synthesis method is novel and more suitable than those already known in the art.